Apparatus and methods for performing handover of user equipment between different radio access networks

ABSTRACT

Aspects of the present disclosure are directed to a user equipment, an RNC, or an application operable in a wireless communications network and methods. A network controller for wireless communication is configured to transfer data via a first user plane connection in a first radio access network and initiate a handover procedure of transferring the user equipment to a second user plane connection in a second radio access network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of provisionalpatent application No. 61/567,549, entitled IMPROVING PERFORMANCE OFDATA APPLICATIONS WHEN UE IS MOVED FROM HSPA TO LTE, filed in the UnitedStates patent office on Dec. 6, 2011, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly, to handover of a userequipment between different radio access networks.

BACKGROUND

Wireless communication networks are widely deployed to provide variouscommunication services such as telephony, video, data, messaging,broadcasts, and so on. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. One example of such a network is the UMTSTerrestrial Radio Access Network (UTRAN). The UTRAN is the radio accessnetwork (RAN) defined as a part of the Universal MobileTelecommunications System (UMTS), a third generation (3G) mobile phonetechnology supported by the 3rd Generation Partnership Project (3GPP).UMTS, which is the successor to Global System for Mobile Communications(GSM) technologies, currently supports various air interface standards,such as Wideband-Code Division Multiple Access (WCDMA), TimeDivision-Code Division Multiple Access (TD-CDMA), and TimeDivision-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS alsosupports enhanced 3G data communications protocols, such as High SpeedPacket Access (HSPA), which provides higher data transfer speeds andcapacity to associated UMTS networks.

As the demand for mobile broadband access continues to increase,research and development continue to advance the wireless communicationtechnologies not only to meet the growing demand for mobile broadbandaccess, but to advance and enhance the user experience with mobilecommunications. An example of an emerging telecommunication standard isthe evolved UTRAN (eUTRAN), also sometimes referred to as Long TermEvolution (LTE). LTE is a set of enhancements to the UMTS mobilestandard promulgated by Third Generation Partnership Project (3GPP). Itis designed to better support mobile broadband Internet access byimproving spectral efficiency, lower costs, improve services, make useof new spectrum, and better integrate with other open standards usingOFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. Therefore, itis desirable that a user equipment is operable in multiple radio accessnetworks, for example, the UTRAN as well as the eUTRAN.

SUMMARY

The following presents a simplified summary of one or more aspects ofthe present disclosure, in order to provide a basic understanding ofsuch aspects. This summary is not an extensive overview of allcontemplated features of the disclosure, and is intended neither toidentify key or critical elements of all aspects of the disclosure norto delineate the scope of any or all aspects of the disclosure. Its solepurpose is to present some concepts of one or more aspects of thedisclosure in a simplified form as a prelude to the more detaileddescription that is presented later.

Aspects of the present disclosure are directed to a user equipment (UE),a radio network controller (RNC), or a remote server operable in awireless communications network and methods in which packet drops may beavoided or reduced during the handover of the UE from one radio accesstechnology (RAT) to another RAT (hereafter Inter-RAT handover).

In one aspect, the disclosure provides a method of wirelesscommunication. The method includes transferring data at a networkcontroller (e.g., an RNC or an eNode B) for a user equipment via a firstuser plane connection in a first radio access network; and if the datatransferred via the first user plane connection satisfies a triggercondition, initiating a handover procedure of transferring the userequipment to a second user plane connection in a second radio accessnetwork.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for transferring data at anetwork controller for a user equipment via a first user planeconnection in a first radio access network; and if the data transferredvia the first user plane connection satisfies a trigger condition, meansfor initiating a handover procedure of transferring the user equipmentto a second user plane connection in a second radio access network.

Another aspect of the disclosure provides a computer-readable storagemedium including code for causing a network controller to: transfer datafor a user equipment via a first user plane connection in a first radioaccess network; and if the data transferred via the first user planeconnection satisfies a trigger condition, initiate a handover procedureof transferring the user equipment to a second user plane connection ina second radio access network.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes at least one processor; and amemory coupled to the at least one processor. The at least one processoris configured to: transfer data for a user equipment via a first userplane connection in a first radio access network; and if the datatransferred via the first user plane connection satisfies a triggercondition, initiate a handover procedure of transferring the userequipment to a second user plane connection in a second radio accessnetwork.

Another aspect of the disclosure provides a method of wirelesscommunication. The method includes transferring data at a networkcontroller for a user equipment via a first user plane connection in afirst radio access network, and initiating a handover procedure oftransferring the user equipment to a second user plane connection in asecond radio access network. In this aspect, the handover procedureincludes relaying a request from the user equipment to a remote serverin data communication with the user equipment, to stop sending data tothe user equipment via the first user plane connection.

Another aspect of the disclosure provides a method of wirelesscommunication. The method includes transferring data at a networkcontroller for a user equipment via a first user plane connection in afirst radio access network, and initiating a handover procedure oftransferring the user equipment to a second user plane connection in asecond radio access network. In this aspect, the handover procedureincludes: initiating the second user plane connection between the userequipment and a remote server via the second radio access network; andtransmitting a request to the remote server to restart transmission ofthe data via the second user plane connection, starting with a packetfollowing in sequence after a last packet received by the user equipmentvia the first user plane connection.

Another aspect of the disclosure provides a method of wirelesscommunication. The method includes transferring data at a networkcontroller for a user equipment via a first user plane connection in afirst radio access network, and initiating a handover procedure oftransferring the user equipment to a second user plane connection in asecond radio access network. In this aspect, the handover procedureincludes initiating the second user plane connection for the userequipment in the second radio access network prior to transmitting ahandover command to the user equipment, and transmitting the handovercommand to the user equipment to release the first user planeconnection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for transferring data for auser equipment via a first user plane connection in a first radio accessnetwork, and means for initiating a handover procedure of transferringthe user equipment to a second user plane connection in a second radioaccess network. In this aspect, the means for initiating the handoverprocedure includes means for relaying a request from the user equipmentto a remote server in data communication with the user equipment, tostop sending data to the user equipment via the first user planeconnection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for transferring data for auser equipment via a first user plane connection in a first radio accessnetwork, and means for initiating a handover procedure of transferringthe user equipment to a second user plane connection in a second radioaccess network. In this aspect, the means for initiating the handoverprocedure includes: means for initiating the second user planeconnection between the user equipment and a remote server via the secondradio access network; and means for transmitting a request to the remoteserver to restart transmission of the data via the second user planeconnection, starting with a packet following in sequence after a lastpacket received by the user equipment via the first user planeconnection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for transferring data for auser equipment via a first user plane connection in a first radio accessnetwork, and means for initiating a handover procedure of transferringthe user equipment to a second user plane connection in a second radioaccess network. In this aspect, the means for initiating the handoverprocedure includes means for initiating the second user plane connectionfor the user equipment in the second radio access network prior totransmitting a handover command to the user equipment, and means fortransmitting the handover command to the user equipment to release thefirst user plane connection.

Another aspect of the disclosure provides a computer-readable storagemedium. The computer-readable storage medium includes code for causing anetwork controller to: transfer data for a user equipment via a firstuser plane connection in a first radio access network; and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In this aspect, inthe handover procedure, the network controller is configured to relay arequest from the user equipment to a remote server in data communicationwith the user equipment, to stop sending data to the user equipment viathe first user plane connection.

Another aspect of the disclosure provides a computer-readable storagemedium. The computer-readable storage medium includes code for causing anetwork controller to transfer data for a user equipment via a firstuser plane connection in a first radio access network, and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In this aspect, inthe handover procedure, the network controller is configured to:initiate the second user plane connection between the user equipment anda remote server via the second radio access network; and transmit arequest to the remote server to restart transmission of the data via thesecond user plane connection, starting with a packet following insequence after a last packet received by the user equipment via thefirst user plane connection.

Another aspect of the disclosure provides a computer-readable storagemedium. The computer-readable storage medium includes code for causing anetwork controller to transfer data for a user equipment via a firstuser plane connection in a first radio access network, and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In this aspect, inthe handover procedure, the network controller is configured to initiatethe second user plane connection for the user equipment in the secondradio access network prior to transmitting a handover command to theuser equipment, and transmit the handover command to the user equipmentto release the first user plane connection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes at least one processor and amemory coupled to the at least one processor. The at least one processoris configured to transfer data for a user equipment via a first userplane connection in a first radio access network, and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In the handoverprocedure, the at least one processor is configured to relay a requestfrom the user equipment to a remote server in data communication withthe user equipment, to stop sending data to the user equipment via thefirst user plane connection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes at least one processor and amemory coupled to the at least one processor. The at least one processoris configured to transfer data for a user equipment via a first userplane connection in a first radio access network, and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In the handoverprocedure, the at least one processor is configured to: initiate thesecond user plane connection between the user equipment and a remoteserver via the second radio access network; and transmit a request tothe remote server to restart transmission of the data via the seconduser plane connection, starting with a packet following in sequenceafter a last packet received by the user equipment via the first userplane connection.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes at least one processor and amemory coupled to the at least one processor. The at least one processoris configured to transfer data for a user equipment via a first userplane connection in a first radio access network, and initiate ahandover procedure of transferring the user equipment to a second userplane connection in a second radio access network. In the handoverprocedure, the at least one processor is configured to initiate thesecond user plane connection for the user equipment in the second radioaccess network prior to transmitting a handover command to the userequipment, and transmit the handover command to the user equipment torelease the first user plane connection.

These and other aspects of the invention will become more fullyunderstood upon a review of the detailed description, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of atelecommunications system.

FIG. 2 is a conceptual diagram illustrating an example of a hardwareimplementation for a user equipment (UE) employing a processing system.

FIG. 3 is a conceptual diagram illustrating an example of a hardwareimplementation for an RNC employing a processing system.

FIG. 4 is a conceptual diagram illustrating an example of a hardwareimplementation for an eNode B (eNB) employing a processing system.

FIG. 5 is a drawing conceptually illustrating an example of a radioaccess network (RAN).

FIG. 6 is a diagram illustrating an example of a third generation (3G)radio protocol architecture.

FIG. 7 is a diagram illustrating an example of a fourth generation (4G)radio protocol architecture.

FIG. 8 is a flowchart illustrating a technique for handling Inter-RAThandover between a UTRAN and an eUTRAN according to an example of thedisclosure.

FIG. 9 is a flowchart illustrating procedures of moving an UE from aUTRAN to an eUTRAN while avoiding or reducing packets drop according toan example of the disclosure.

FIG. 10 is a flowchart illustrating procedures of fast recovery on theeUTRAN side after an Inter-RAT handover when packets are allowed to dropduring the handover.

FIG. 11 is a diagram illustrating mobility procedures of moving a UEfrom a UTRAN to an eUTRAN according to the related art.

FIG. 12 is a diagram illustrating mobility procedures of moving a UEfrom a UTRAN to an eUTRAN according to an example of the presentdisclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

According to various aspects of this disclosure, a user equipment (UE)may include hardware and/or software for supporting one or more radioaccess technologies (RATs). For example, a UE may include hardwareand/or software for accessing UMTS/HSPA and Long Term Evolution (LTE)networks. However, when the UE moves between (i.e., handover) differentRATs (e.g., from UMTS/HSPA to LTE) while user data is being transferredbetween the UE and a remote terminal or network entity, packets may bedropped at one of the network nodes such as a radio network controller(RNC). The dropped packets may impact the performance of packet-basedapplications and undesirably affect user experience. In variousillustrative examples described herein, UE based and/or network basedtechniques are utilized to improve handover performance when the UE ismoved from a UMTS/HSPA network to an LTE network. However, the describedtechniques may also be applicable to other types of Inter-RAT handovers(e.g., WiMAX to LTE, EV-DO to HSPA, EV-DO to HSPA, LTE to HSPA, etc.)

According to various aspects of this disclosure, Inter-RAT handover(e.g., HSPA to LTE) may be triggered by various events or conditionssuch as, for example, based on data transferred (e.g., data volumetriggers in a period of time). In addition to data volume triggers,other types of triggers may be used. For example, Inter-RAT handover maybe triggered if one of the network's coverage/quality is better than acertain threshold. However, it should be noted that other examples fortriggering Inter-RAT handover in other implementations may be used.

According to various aspects of this disclosure, potential enhancementsto Inter-RAT handover include avoiding packet drops or recoveringquickly after packet drops through an implementation specific UE basedapproach and/or a change of mobility approach. These enhancements willbe described in more detail infra. The various concepts presentedthroughout this disclosure may be implemented across a broad variety oftelecommunication systems, network architectures, and communicationstandards.

FIG. 1 is a block diagram conceptually illustrating a telecommunicationssystem 100 including a UTRAN and an eUTRAN according to an example ofthe disclosure. Referring now to FIG. 1, the telecommunications system100 may include both UMTS/HSPA and long term evolution (LTE) networkaccess to a user equipment (UE) 101. In one example, thetelecommunications system 100 has an evolved packet core (EPC), a UTRAN102, and an eUTRAN 110. Among several options available for the UTRAN102, in this example, the illustrated UTRAN 102 may employ a WCDMA airinterface for enabling various wireless services including telephony,video, data, messaging, broadcasts, and/or other services. The UTRAN 102may include a plurality of Radio Network Subsystems (RNSs), eachcontrolled by a respective Radio Network Controller (RNC) such as an RNC104. For reasons of clarity, only the RNC 104 is shown in FIG. 1. TheRNC 104 is an apparatus responsible for, among other things, assigning,reconfiguring, and releasing radio resources within an RNS. The RNC 104may be interconnected to other RNCs (not shown) in the UTRAN 102 throughvarious types of interfaces such as a direct physical connection, avirtual network, or the like using any suitable transport network.

The geographic region covered by the RNS may be divided into a number ofcells, with a radio transceiver apparatus serving each cell. A radiotransceiver apparatus is commonly referred to as a Node B in UMTSapplications, but may also be referred to by those skilled in the art asa base station (BS), a base transceiver station (BTS), a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), an access point (AP), or someother suitable terminology. For clarity, one Node B 106 is shown in theUTRAN 102; however, each RNS may include any number of wireless Node Bs.The Node B 106 provides wireless access points to a core network for anynumber of mobile apparatuses (e.g., UE 101). Examples of a mobileapparatus include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a notebook, a netbook, a smartbook, apersonal digital assistant (PDA), a satellite radio, a globalpositioning system (GPS) device, a multimedia device, a video device, adigital audio player (e.g., MP3 player), a camera, a game console, orany other similar functioning device. The mobile apparatus is commonlyreferred to as user equipment (UE) in UMTS and LTE applications, but mayalso be referred to by those skilled in the art as a mobile station(MS), a subscriber station, a mobile unit, a subscriber unit, a wirelessunit, a remote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal (AT), a mobile terminal, a wireless terminal, a remoteterminal, a handset, a terminal, a user agent, a mobile client, aclient, or some other suitable terminology. The UE 101 may furtherinclude a universal subscriber identity module (USIM) (not shown), whichcontains a user's subscription information to a network. Forillustrative purposes, one UE 101 is shown in communication with theNode B 106. The downlink (DL), also called the forward link, refers tothe communication link from the Node B 106 to the UE 101, and the uplink(UL), also called the reverse link, refers to the communication linkfrom the UE 101 to the Node B 106.

The telecommunications system 100 may include a serving GPRS supportnode (SGSN) 109 to provide packet-data services. The SGSN 109 provides apacket-based connection for the UTRAN 102 to the EPC 108.

As shown, an evolved packet core (EPC) 108 can interface with one ormore radio access networks, such as the UTRAN 102 and an evolved UTRAN(eUTRAN) 110. However, as those skilled in the art will recognize, thevarious concepts presented throughout this disclosure may be implementedin other suitable radio access networks, to provide UEs with access totypes of core networks other than UMTS and LTE networks. The eUTRAN 110may include an eNode B (eNB) 112 and other eNBs (not shown). The eNB 112provides user and control plane protocol terminations toward the UE 101.The eNB 112 may be connected to the other eNBs via an X2 interface(i.e., backhaul). The eNB 112 may also be referred to by those skilledin the art as a base station, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), or some other suitableterminology. The eNB 112 provides an access point to the EPC 108 for theUE 101.

The EPC 108 includes a Mobility Management Entity (MME) 114, other MMEs(not shown), a Serving Gateway (S-WG) 116, and a Packet Data Network(PDN) Gateway (P-GW) 118. The MME 114 is the control node that processesthe signaling between the UE 101 and the EPC 108. Generally, the MME 114provides bearer and connection management. All user IP packets aretransferred through the P-GW 116, which itself is connected to the P-GW118. The P-GW 118 provides UE IP address allocation as well as otherfunctions. The P-GW 118 is connected to Operator's IP Services 120. TheOperator's IP Services may be provided by one or more remote servers.The terms Operator's IP Services and remote server(s) may be usedinterchangeably herein. The Operator's IP Services 120 may include theInternet, the Intranet, an IP Multimedia Subsystem (IMS), and a PSStreaming Service (PSS). In one example, the IP Services 120 include aTCP server. The telecommunications network 100 may include a HomeSubscriber Server (HSS) 122 that presents the registers, coveringfunctionalities such as the Home Location Register (HLR) and contains,for example, user-specific information on service priorities, datarates, etc. The S-GW 116 and P-GW 118 handle tasks related to themobility management inside the eUTRAN 110, as well as the UTRAN 102. Asshown in FIG. 1, the SGSN 109 is operatively connected to the gateways116 and 118, thus handling the Gateway GPRS Support Node (GGSN)functionalities of the UTRAN network.

FIG. 2 is a conceptual diagram illustrating a hardware implementationfor the UE 101 according to an example of the disclosure. Components ofthe UE 101 generally known in the art are not shown for reasons ofclarity and comprehensibility. As shown in FIG. 2, the UE 101 generallyincludes a processing circuit 202 coupled to or placed in electricalcommunication with a communications interface 204 and a storage medium206.

The processing circuit 202 is arranged to obtain, process and/or senddata, control data access and storage, issue commands, and control otherdesired operations. The processing circuit 202 may include circuitryadapted to implement desired programming provided by appropriate mediain at least one example. For example, the processing circuit 202 may beimplemented as one or more processors, one or more controllers, and/orother structures configured to execute executable programming Examplesof the processing circuit 202 may include a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic component, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general purpose processor mayinclude a microprocessor, as well as any conventional processor,controller, microcontroller, or state machine. The processing circuit202 may also be implemented as a combination of computing components,such as a combination of a DSP and a microprocessor, a number ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, an ASIC and a microprocessor, or any other number of varyingconfigurations. These examples of the processing circuit 202 are forillustration and other suitable configurations within the scope of thepresent disclosure are also contemplated.

The processing circuit 202 is adapted for processing, including theexecution of programming, which may be stored on the storage medium 206.As used herein, the term “programming” shall be construed broadly toinclude without limitation instructions, instruction sets, data, code,code segments, program code, programs, subprograms, software modules,applications, software applications, software packages, routines,subroutines, objects, executables, threads of execution, procedures,functions, etc., whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise.

The communications interface 204 is configured to facilitate wirelesscommunications of the UE 101. For example, the communications interface204 may include circuitry and/or programming adapted to facilitate thecommunication of information bi-directionally with respect to one ormore network nodes. The communications interface 204 may be coupled toone or more antennas (not shown), and includes wireless transceivercircuitry, including at least one receiver circuit 208 (e.g., one ormore receiver chains) and/or at least one transmitter circuit 210 (e.g.,one or more transmitter chains).

The storage medium 206 may represent one or more computer-readable,machine-readable, and/or processor-readable devices for storingprogramming, such as processor executable code or instructions (e.g.,software, firmware), electronic data, databases, or other digitalinformation. The storage medium 206 may also be used for storing datathat is manipulated by the processing circuit 202 when executingprogramming. The storage medium 206 may be any available media that canbe accessed by a general purpose or special purpose processor, includingportable or fixed storage devices, optical storage devices, and variousother mediums capable of storing, containing and/or carrying programmingBy way of example and not limitation, the storage medium 206 may includea computer-readable, machine-readable, and/or processor-readable storagemedium such as a magnetic storage device (e.g., hard disk, floppy disk,magnetic strip), an optical storage medium (e.g., compact disk (CD),digital versatile disk (DVD)), a smart card, a flash memory device(e.g., card, stick, key drive), random access memory (RAM), read onlymemory (ROM), programmable ROM (PROM), erasable PROM (EPROM),electrically erasable PROM (EEPROM), a register, a removable disk,and/or other mediums for storing programming, as well as any combinationthereof.

The storage medium 206 may be coupled to the processing circuit 202 suchthat the processing circuit 202 can read information from, and writeinformation to, the storage medium 206. That is, the storage medium 206can be coupled to the processing circuit 202 so that the storage medium206 is at least accessible by the processing circuit 202, includingexamples where the storage medium 206 is integral to the processingcircuit 202 and/or examples where the storage medium 206 is separatefrom the processing circuit 202 (e.g., resident in the UE 101, externalto the UE 101, and/or distributed across multiple entities).

Programming stored by the storage medium 206, when executed by theprocessing circuit 202, causes the processing circuit 202 to perform oneor more of the various functions and/or process steps described herein.For example, the storage medium 206 may include a handover routine 212that may be executed by the processing circuit 202 (e.g., a handovercircuitry 216) to handle Inter-RAT handovers. Thus, according to one ormore aspects of the present disclosure, the processing circuit 202 isadapted to perform (in conjunction with the storage medium 206) any orall of the processes, functions, steps and/or routines for any or all ofthe UEs described herein (e.g., UE 101). As used herein, the term“adapted” in relation to the processing circuit 202 may refer to theprocessing circuit 202 being one or more of configured, employed,implemented, and/or programmed to perform a particular process,function, step and/or routine according to various features describedherein.

FIG. 3 is a conceptual diagram illustrating a hardware implementation ofthe RNC 104 according to an example of the disclosure. Components of theRNC 104 generally known in the art are not shown for reasons of clarityand comprehensibility. As shown, the RNC 104 includes a processingcircuit 302 coupled to or placed in electrical communication with acommunications interface 304 and to a storage medium 306. The processingcircuit 302 is arranged to obtain, process and/or send data, controldata access and storage, issue commands, and control other desiredoperations. The processing circuit 302 may include circuitry adapted forprocessing, including the execution and implementation of programmingprovided by appropriate media, including media stored on the storagemedium 306 in at least one example. Examples and implementations for theprocessing circuit 302 may include any of the various examples andimplementations of the processing circuit 202 described above withreference to FIG. 2. The examples of the processing circuit 302including those set forth with reference to the processing circuit 202in FIG. 2 are for illustration, and other suitable configurations withinthe scope of the present disclosure are also contemplated.

The communications interface 304 is configured to facilitate wiredand/or wireless communications of the RNC 104. For example, thecommunications interface 304 may include circuitry and/or programmingadapted to facilitate the communication of information bi-directionallywith respect to one or more UEs, as well as one or more other networknodes. The communications interface 304 may be coupled to one or moreantennas (not shown), and includes wireless transceiver circuitry,including at least one receiver circuit 308 (e.g., one or more receiverchains) and/or at least one transmitter circuit 310 (e.g., one or moretransmitter chains).

The storage medium 306 may represent one or more computer-readable,machine-readable, and/or processor-readable devices for storingprogramming, such as processor executable code or instructions (e.g.,software, firmware), electronic data, databases, or other digitalinformation. The storage medium 306 may also be used for storing datathat is manipulated by the processing circuit 302 when executingprogramming. The storage medium 306 may be any available media that canbe accessed by a general purpose or special purpose processor, includingportable or fixed storage devices, optical storage devices, and variousother mediums capable of storing, containing and/or carryingprogramming. Examples of the storage medium 306 may include any of theexamples included in the description of the storage medium 206 set forthabove with reference to FIG. 2.

The storage medium 306 may be coupled to the processing circuit 302 suchthat the processing circuit 302 can read information from, and writeinformation to, the storage medium 306. That is, the storage medium 306can be coupled to the processing circuit 302 so that the storage medium306 is at least accessible by the processing circuit 302, includingexamples where the storage medium 306 is integral to the processingcircuit 302 and/or examples where the storage medium 306 is separatefrom the processing circuit 302 (e.g., resident in the RNC 104, externalto the RNC 104, and/or distributed across multiple entities).

Programming stored by the storage medium 306, when executed by theprocessing circuit 302, causes the processing circuit 302 to perform oneor more of the various functions and/or process steps described herein.For example, the storage medium 306 may include an Inter-RAT routine312, and the processing circuit 102 may include a handover circuitry 314that is adapted to perform various functions in accordance with theInter-RAT routine 312. The various functions of the Inter-RAT routine312 will be described in more detail infra. Thus, according to one ormore aspects of the present disclosure, the processing circuit 302 isadapted to perform (in conjunction with the storage medium 306) any orall of the processes, functions, steps and/or routines for any or all ofthe RNC 104 described herein. As used herein, the term “adapted” inrelation to the processing circuit 302 may refer to the processingcircuit 302 being one or more of configured, employed, implemented,and/or programmed to perform a particular process, function, step and/orroutine according to various features described herein.

FIG. 4 is a conceptual diagram illustrating a hardware implementation ofthe eNB 112 according to an example of the disclosure. Components of theeNB 112 generally known in the art are not shown for reasons of clarityand comprehensibility. As shown, the eNB 112 includes a processingcircuit 402 coupled to or placed in electrical communication with acommunications interface 404 and to a storage medium 406. The processingcircuit 402 is arranged to obtain, process and/or send data, controldata access and storage, issue commands, and control other desiredoperations. The processing circuit 402 may include circuitry adapted forprocessing, including the execution and implementation of programmingprovided by appropriate media, including media stored on the storagemedium 406 in at least one example. Examples and implementations for theprocessing circuit 402 may include any of the various examples andimplementations of the processing circuit 202 described above withreference to FIG. 2. The examples of the processing circuit 402including those set forth with reference to the processing circuit 202in FIG. 2 are for illustration, and other suitable configurations withinthe scope of the present disclosure are also contemplated.

The communications interface 404 is configured to facilitate wiredand/or wireless communications of the eNB 112. For example, thecommunications interface 404 may include circuitry and/or programmingadapted to facilitate the communication of information bi-directionallywith respect to one or more UEs, as well as one or more other networknodes. The communications interface 404 may be coupled to one or moreantennas (not shown), and includes wireless transceiver circuitry,including at least one receiver circuit 408 (e.g., one or more receiverchains) and/or at least one transmitter circuit 410 (e.g., one or moretransmitter chains).

The storage medium 406 may represent one or more computer-readable,machine-readable, and/or processor-readable devices for storingprogramming, such as processor executable code or instructions (e.g.,software, firmware), electronic data, databases, or other digitalinformation. The storage medium 406 may also be used for storing datathat is manipulated by the processing circuit 402 when executingprogramming. The storage medium 406 may be any available media that canbe accessed by a general purpose or special purpose processor, includingportable or fixed storage devices, optical storage devices, and variousother mediums capable of storing, containing and/or carryingprogramming. Examples of the storage medium 406 may include any of theexamples included in the description of the storage medium 206 set forthabove with reference to FIG. 2.

The storage medium 406 may be coupled to the processing circuit 402 suchthat the processing circuit 402 can read information from, and writeinformation to, the storage medium 406. That is, the storage medium 406can be coupled to the processing circuit 402 so that the storage medium406 is at least accessible by the processing circuit 402, includingexamples where the storage medium 406 is integral to the processingcircuit 402 and/or examples where the storage medium 406 is separatefrom the processing circuit 402 (e.g., resident in the eNB 112, externalto the eNB 112, and/or distributed across multiple entities).

Programming stored by the storage medium 406, when executed by theprocessing circuit 402, causes the processing circuit 402 to perform oneor more of the various functions and/or process steps described herein.For example, the storage medium 406 may include an Inter-RAT routine412, and the processing circuit 402 may include a handover circuitry 414that is adapted to perform various functions in accordance with theInter-RAT routine 412. The various functions of the Inter-RAT routine412 will be described in more detail infra. Thus, according to one ormore aspects of the present disclosure, the processing circuit 402 isadapted to perform (in conjunction with the storage medium 406) any orall of the processes, functions, steps and/or routines for any or all ofthe eNB 112 described herein. As used herein, the term “adapted” inrelation to the processing circuit 402 may refer to the processingcircuit 402 being one or more of configured, employed, implemented,and/or programmed to perform a particular process, function, step and/orroutine according to various features described herein.

FIG. 5 is a drawing conceptually illustrating an example of a radioaccess network (RAN) 500 supporting multiple RATs (e.g., UTRAN andeUTRAN) that may be utilized in accordance with the present disclosure.The RAN 500 includes multiple cellular regions (cells), including cells502, 504, and 506, each of which may include one or more sectors. Cellsmay be defined geographically (e.g., by coverage area) and/or may bedefined in accordance with a frequency, scrambling code, etc. That is,the illustrated geographically-defined cells 502, 504, and 506 may eachbe further divided into a plurality of cells

In a cell that is divided into sectors, the multiple sectors within acell can be formed by groups of antennas with each antenna responsiblefor communication with UEs in a portion of the cell. For example, incell 502, antenna groups 512,514, and 516 may each correspond to adifferent sector. In cell 504, antenna groups 518, 520, and 522 may eachcorrespond to a different sector. In cell 506, antenna groups 524, 526,and 528 may each correspond to a different sector.

The cells 502, 504, and 506 may include several UEs that may be incommunication with one or more sectors of each cell 502, 504, or 506.For example, UEs 530 and 532 may be in communication with Node B/eNB542, UEs 534 and 536 may be in communication with Node B/eNB 544, andUEs 538 and 540 may be in communication with Node B/eNB 546. Here, eachNode B/eNB 542, 544, and 546 may be configured to provide an accesspoint to a EPC 108 (see FIG. 1) for all the UEs 530, 532, 534, 536, 538,and 540 in the respective cells 502, 504, and 506. In various examples,each of the Node B/eNB 542, 544, and 546 may include a Node B 106, aneNB 112, or both. In some examples, a Node B and an eNB of the same cellmay be at the same location or different locations. That is, a coveragearea of a Node B (e.g., 504 a) and that of a corresponding eNB (e.g.,504 b) may overlap each other, partially overlap each other, or do notoverlap. Therefore, the RAN 500 may support multiple radio accessnetworks such as the HSPA and LTE standards.

Recently, many existing networks have been upgraded to support both UMTSand LTE. Therefore, a UE 101 configured to support multiple RATs maymove from one RAT to another RAT (Inter-RAT handover) in the middle ofan ongoing communication. However, when the UE 101 moves from one RAT toanother RAT, data packets may be dropped at one or more of the networknodes (e.g., RNC 104). This can impact certain applications such asTCP-based applications. Aspects of this disclosure describe UE-based andnetwork-based techniques that may enhance performance of TCP and otherdata applications when the UE 101 is moved from one RAT to another RAT,by way of example, from HSPA to LTE

In a wireless telecommunications system, the communication protocolarchitecture may take on various forms depending on the particularapplication. For example, in a 3GPP UMTS network, the signaling protocolstack is divided into a Non-Access Stratum (NAS) and an Access Stratum(AS). The NAS provides the upper layers, for signaling between the UE101 and the core network, and may include circuit switched and packetswitched protocols. The AS provides the lower layers, for signalingbetween the UTRAN/eUTRAN and the UE 101, and may include a user planeand a control plane. Here, the user plane (also referred to herein asthe data plane) carries user traffic, while the control plane carriescontrol information (i.e., signaling).

FIG. 6 is a diagram illustrating an example of a radio protocolarchitecture operational in a UMTS network. Turning to FIG. 6, the AS isshown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 is thelowest layer and implements various physical layer signal processingfunctions. Layer 1 will be referred to herein as the physical layer 606.The data link layer, called Layer 2 608, is above the physical layer 606and is responsible for the link between the UE 101 and Node B 106 overthe physical layer 606.

At Layer 3, the RRC layer 616 handles the control plane signalingbetween the UE 101 and the Node B 106. RRC layer 616 includes a numberof functional entities for routing higher layer messages, handlingbroadcasting and paging functions, establishing and configuring radiobearers, etc.

In the illustrated air interface, the L2 layer 608 is split intosublayers. In the control plane, the L2 layer 608 includes twosublayers: a medium access control (MAC) sublayer 610 and a radio linkcontrol (RLC) sublayer 612. In the user plane, the L2 layer 608additionally includes a packet data convergence protocol (PDCP) sublayer614. Although not shown, the UE 101 may have several upper layers abovethe L2 layer 608 including a network layer (e.g., IP layer) that isterminated at a PDN gateway on the network side and an application layerthat is terminated at the other end of the connection (e.g., far end UE,server, etc.).

The PDCP sublayer 614 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 614 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between Node Bs.

The RLC sublayer 612 generally supports an acknowledged mode (AM) (wherean acknowledgment and retransmission process may be used for errorcorrection), an unacknowledged mode (UM), and a transparent mode fordata transfers, and provides segmentation and reassembly of upper layerdata packets and reordering of data packets to compensate forout-of-order reception due to a hybrid automatic repeat request (HARQ)at the MAC layer. In the acknowledged mode, RLC peer entities such as anRNC and a UE may exchange various RLC protocol data units (PDUs)including RLC Data PDUs, RLC Status PDUs, and RLC Reset PDUs, amongothers. In the present disclosure, the term “packet” may refer to anyRLC PDU exchanged between RLC peer entities.

The MAC sublayer 610 provides multiplexing between logical and transportchannels. The MAC sublayer 610 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 610 is also responsible for HARQ operations.

FIG. 7 is a diagram illustrating an example of a radio protocolarchitecture operable in an LTE network. Turning to FIG. 7, the radioprotocol architecture for communication between the UE 101 and the eNB112 is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1is the lowest layer and implements various physical layer signalprocessing functions. Layer 1 will be referred to herein as the physicallayer 706. Layer 2 (L2 layer) 708 is above the physical layer 706 and isresponsible for the link between the UE 101 and eNB 112 over thephysical layer 706. In the user plane, the L2 layer 708 includes a mediaaccess control (MAC) sublayer 710, a radio link control (RLC) sublayer712, and a packet data convergence protocol (PDCP) 714 sublayer, whichare terminated at the eNB 112 on the network side. Although not shown,the UE 101 may have several upper layers above the L2 layer 708including a network layer (e.g., IP layer) that is terminated at theP-GW 118 (see FIG. 1) on the network side, and an application layer thatis terminated at the other end of the connection (e.g., far end UE,server, etc.).

The PDCP sublayer 714 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 714 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 712 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 710 provides multiplexing between logical and transportchannels. The MAC sublayer 710 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 710 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE 101 andeNB 112 is substantially the same for the physical layer 706 and the L2layer 708 with the exception that there is no header compressionfunction for the control plane. The control plane also includes a radioresource control (RRC) sublayer 716 in Layer 3. The RRC sublayer 716 isresponsible for obtaining radio resources (i.e., radio bearers) and forconfiguring the lower layers using RRC signaling between the eNB and theUE.

Hereinafter, various aspects of the disclosure are described in thefollowing nonlimiting examples in which the UE 101 may include hardwareand/or software for supporting multiple RATs. By way of example, and notlimited thereto, the UE 101 may include hardware and/or software forsupporting both HSPA and LTE standards. When the UE 101 moves from HSPAto LTE, packets may be dropped at one of the network nodes (e.g., theRNC 104). Therefore, according to aspects of the present disclosure, UEbased and network based techniques are used to enhance the performanceof data application (e.g., TCP applications) when the UE 101 is movedfrom HSPA to LTE. The below described techniques may also be applicableto other types of Inter-RAT handovers (e.g., WiMAX to LTE, EV-DO toHSPA, EV-DO to HSPA, LTE to HSPA, etc.)

In one aspect of the disclosure, Inter-RAT handover (e.g., HSPA to LTE)may be triggered by various events, such as, for example, based on datavolume triggers. FIG. 8 is a flowchart illustrating a process 800 forhandling an Inter-RAT handover from HSPA to LTE. According to someaspects of the disclosure, by way of example only, a UE 101 including ahandover routine 212, an RNC 104 including an Inter-RAT routine 312, andan eNobeB 112 including an Inter-RAT routine 412 may be operated toperform the procedures described in FIG. 8.

Referring to the process 800, at step 802, the UE 101 is initiallycamped on a UTRAN 102. At step 804, the UE 101 is transferring datausing HSPA (e.g., downloading data from a remote server or anapplication server). For example, the UE 101 may be downloading a filefrom a remote server or an application server using a TCP connection viaHSPA. At step 806, if a certain handover or trigger condition is met,the UE 101 is moved from the UTRAN 102 to an eUTRAN 110. In one aspect,the Inter-RAT routine 312 of the RNC 104 may include suitable functionsfor monitoring the handover condition. For example, if the UE 101 isdownloading a volume of data exceeding a threshold (e.g., apredetermined threshold) within a period of time, and the UE 101 iscamped on the UTRAN, an Inter-RAT handover may be triggered to move theUE 101 from the UTRAN to the eUTRAN at step 808.

In one aspect, the Inter-RAT routine 312 may include suitable functionsfor sending a command to the UE 101 to commence handover to the eNodeB112. Upon the reception of the command, the UE 101 according to thehandover routine 212 suspends transmission of user plane data and movesto the eUTRAN 110 and performs suitable access procedures toward thetarget eNodeB 112. When the UE 101 has gotten access to the eNodeB 112,the handover routine 212 of the UE may include suitable functions forsending a message to alert the eNodeB 112. Upon reception of the messagefrom the UE 101, the Inter-RAT routine 412 of the eNodeB 112 may includesuitable functions for completing the Inter-RAT handover.

In one example, the threshold may be about 500 Kbytes or other suitablevalues. The period of time may be selected to be about 15 seconds orother suitable time periods. It should be noted that this is but onecondition for triggering the Inter-RAT handover, and other suitabletriggers may be used in other implementations. In various examples, inaddition to downlink triggers, uplink traffic volume measurement (TVM)triggers may be used. In still other examples, a combination of downlinkand uplink TVM triggers may be used.

In addition to data volume triggers, according to other aspects of thedisclosure, other types of handover triggers may be used. For example,if the LTE coverage/quality is better than a certain threshold (e.g.,based on compressed mode (CM) measurements or other implementation basedtechniques, such as estimated signal strength on collocated UMTS cell),Inter-RAT handover may be triggered to move the UE 101 from the UTRAN tothe eUTRAN. For example, the signal quality may be an evolved UMTSterrestrial radio access (E-UTRA) reference signal receiver quality(RSRQ), an E-UTRA reference signal received power (RSRP), or acombination thereof. At step 808, the UE 101 may revert to the UTRANunder certain conditions. For example, the eUTRAN coverage/quality maybe below a certain threshold, the amount of data transferred by the UE101 in a period of time is below a certain threshold, or other suitableconditions, triggers, or combinations thereof may be considered.

Thresholds such as those discussed above may be chosen to allow smallweb page and/or file downloads (e.g., social media updates, instantmessaging (IM) sessions, mobile web pages downloads, etc.) to be handledby the UTRAN. The UE 101 may then be moved (handover) to the eUTRAN, forexample, only for medium to large file downloads and heavy streaming(e.g., audio and/or video streaming)

However, pursuant to how current handover procedures are implemented ina communications system, when the UE 101 is moved from the UTRAN to theeUTRAN, or vice-versa, packets buffered at the RNC 104 in the UTRAN maybe dropped if either (a) redirection is used or (b) Packet SwitchedHandover (PSHO) is used, and Inter-RAT data forwarding is not supported.This will lead to the TCP window being cut and can reduce the rate ofgrowth of the TCP window in LTE. Therefore, performance degradation ofthe applications may be perceived by the user of the UE 101. Inaccordance with various aspects of the present disclosure, enhancementsto the Inter-RAT handover (e.g., UTRAN to eUTRAN handover) are provided.These enhancements include UE-based and network-based techniques. UsingUE-based techniques, “implementation specific” UE procedures may be usedto (a) avoid packet drops at the RNC 104 or (b) allow packet drops atthe RNC 104 but recover faster in the LTE side. Using network-basedtechniques, packet drops at the RNC 104 may be avoided through a changein mobility procedures. The following examples will provide a moredetailed description of these techniques.

FIG. 9 is a flowchart 900 illustrating an exemplary procedure of movingthe UE 101 from the UTRAN to the eUTRAN while avoiding or reducingpackets drop. By way of example, the procedures illustrated with FIG. 9may be implemented by the block 808 of FIG. 8. Referring to FIG. 9, in902, an RNC 104 determines that the UE 101 is to be moved from UTRAN toeUTRAN based on one or more of the above-described trigger conditions orother suitable conditions. For example, the UE 101 is transferring datawith a remote server 120 via HSPA. Then, in 904, the UE 101 sends a stopmessage to the remote server to request the remote server to stopsending data to the UE 101. In one aspect of the disclosure, thehandover routine 212 of the UE 101 may include suitable functions forsending the stop message to the remote server 120. In one example, theUE 101 may be in data communication with a TCP server through the UTRAN,and the UE 101 may transmit a stop message (e.g., receive window sizeequal zero message hereafter “receive window=0”) to the TCP serverbefore commencing handover. In 906, responsive to the stop message, theremote server stops sending any more packets to the UE 101. In 908,handover may proceed to move the UE 101 from the UTRAN to the eUTRAN.For example, the routine 212 of the UE 101 may include suitablefunctions for carrying out the handover procedures.

However, there may be packets still in the data path because the remoteserver may have sent some more packets before the stop message isreceived. For example, some packets may be at the RNC 104 or othernetwork nodes between the UE 101 and the remote server 120. Therefore,the stop message (e.g., “receive window=0”) is sent sufficiently inadvance by the UE 101. In some examples, an appropriate trigger may beused for sending the “receive window=0” message to the remote server 120sufficiently in advance of the Inter-RAT handover. According to someaspects of the disclosure, suitable triggers may be mobility events inHSPA or LTE, or events leading to mobility events.

FIG. 10 is a flowchart 1000 illustrating the procedures of fast recoveryon the eUTRAN side after an Inter-RAT handover when packets are allowedto drop during the handover. Different from the procedures of FIG. 9,the UE 101 may not send a stop message to a remote server beforecommencing handover. By way of example, the procedures illustrated inFIG. 10 may be implemented in the block 808 of FIG. 8. Referring to FIG.10, in 1002, the UE 101 is to be moved from the UTRAN to the eUTRANbased on one or more of the above-described trigger conditions or othersuitable conditions, for example, as set forth in reference to block806. At this time, the UE 101 is transferring data with a remote server120 via HSPA. Therefore, packets may be dropped at one or more of thenetwork nodes when the UE 101 is moved from the UTRAN to the eUTRAN. In1004, after the UE 101 is moved from the UTRAN to the eUTRAN (e.g.,initiated by the RNC 104 executing the Inter-RAT routine 312 as setforth in reference to block 808), the UE 101 starts a new dataconnection (e.g., TCP connection) with the remote server 120 on theeUTRAN. Here, the handover of the UE 101 from the UTRAN to the eUTRANcan be accomplished by procedures generally known in the art.

In one example, the UE 101 may be configured to transfer files with theremote server 120 using a file transfer application (e.g., file transferapplications using the file transfer protocol (FTP)). Such file transferapplication supports commands to retrieve only a part of the file. In1006, by way of example, after the UE 101 started a new TCP connectionwith the remote server 120 on the eUTRAN, the UE 101 may request theremote server 120 to send data starting from the point the UE 101 hasalready downloaded on the previous TCP connection on HSPA before thehandover. In 1008, the remote server 120 resumes data transfer startingfrom the requested point. When the technique illustrated in FIG. 10 areused for some or all of the commonly used applications (file transfer,streaming, etc.), it would likely cover a large percentage of cases,hence the handover performance may be enhanced. In some examples, thistechnique may involve some interaction with the UE's operating system(OS) or suitable modifications thereof.

According to other aspects of the disclosure, the mobility proceduresmay be modified to avoid dropping packets at the RNC 104 duringInter-RAT handover. FIG. 11 is a diagram illustrating some mobilityprocedures of moving the UE 101 from the UTRAN to the eUTRAN accordingto the related art. For example, more detail of the procedures aredefined in the 3GPP Technical Specification 23.401 V11.3.0 (2012September ), Release 11, Sections 5.5.2.2.2 to 5.5.2.2.3, which ishereby incorporated by reference in its entirety.

Referring to FIG. 11, a source RNC 104 decides to initiate an Inter-RAThandover from the UTRAN to the eUTRAN based on one or more of thetrigger conditions described in reference to FIG. 8. At this point, bothuplink and/or downlink user data may be transmitted via the following:bearer(s) 1102 between the UE 101 and the source RNC 104, GPRS tunnelingprotocol (GTP) tunnel(s) 1104 between the source RNC 104, the sourceSGSN 109, the serving gateway (S-GW) 116, and the PDSN gateway (P-GW)118.

In a preparation phase, the source RNC 104 sends a Relocation Requiredmessage to the source SGSN 109 to request the core network to establishresources in a target eNB 112, a target MME 114, and the S-GW 116.During the preparation phrase, the source RNC 104 continues to receivedownlink and/or uplink user plane PDUs. In an execution phase, thesource SGSN 109 sends a message Relocation Command 1106 to the sourceRNC 104. The source RNC 104 will command to the UE 101 to handover tothe target eNB 112 via the message HO from UTRAN Command 1108. Theaccess network specific message to UE includes a transparent containerincluding radio aspect parameters that the target eNB 112 has set-up inthe preparation phase.

Upon the reception of the HO from UTRAN Command message 1108 containingthe Relocation Command message, the UE 101 suspends the uplinktransmission of the user plane data, and moves to the eUTRAN 110 andperforms suitable access procedures toward the target eNB 112. When theUE 101 has gotten access to the target eNB 112, it sends the message HOto eUTRAN Complete 1110 to the target eNB 112. When the UE 101 hassuccessfully accessed the target eNB 112, the target eNB 112 informs thetarget MME 114 by sending the message Handover Notify (TAI+ECGI) 1112.Then, the target MME 114 knows that the UE 101 has arrived at the targetside, and the target MME 114 informs the source SGSN 109 by sending theForward Relocation Complete Notification message 1114. The source SGSN109 also sends an acknowledge message 1116 to the target MME 1114. Thetarget MME 114 will now complete the Inter-RAT handover procedure byinforming the S-GW 116 that the target MME 114 is now responsible forall the bearers the UE 101 have established. This is performed in themessage Modify Bearer Request 1118.

The S-GW 116 acknowledges the user plane switch to the target MME 114via the message Modify Bearer Response 1120. At this stage, the userplane path is established for all bearers between the UE 101, target eNB112, S-GW 116, and P-GW 118. If the S-GW 116 does not change, the S-GW116 shall send one or more “end marker” packets on the old pathimmediately after switching the path in order to assist the reorderingfunction in the target eNB 112. The above-described handover proceduresillustrate some of the relevant steps when a UE is moved from the UTRANto the eUTRAN. One skilled in the relevant art will understand that thehandover procedures include other suitable steps or processes that aregenerally known in the art and are omitted for reasons of clarity andcomprehensibility.

FIG. 12 is a diagram illustrating the mobility procedures of moving theUE 101 from the UTRAN to the eUTRAN according to some aspects of thepresent disclosure. However, the mobility procedures illustrated in FIG.12 may be applicable in other Inter-RAT handovers. Referring to FIG. 12,a source RNC 104 decides to initiate an inter-RAT handover from theUTRAN to the eUTRAN based on one or more of the trigger conditionsdescribed in reference to FIG. 8. At this point, both uplink and/ordownlink user data may be transmitted via the following: bearer(s) 1202between the UE 101 and the source RNC 104, GPRS tunneling protocol (GTP)tunnel(s) 1204 between the source RNC 104, the source SGSN 109, the S-GW116, and the P-GW 118.

In a preparation phase, the source RNC 104 sends a Relocation Requiredmessage to the source SGSN 109 to request the core network to establishresources in a target eNB 112, a target MME 114, and the S-GW 116.During the preparation phrase, the source RNC 104 continues to receivedownlink and/or uplink user plane PDUs. In an execution phase, thesource SGSN 109 may send the message Relocation Command 1206 to thesource RNC 104. The source RNC 104 will command to the UE 101 tohandover to the target eNB 112 via, for example, the message HO fromUTRAN Command. However, before the source RNC 104 sends the message HOfrom UTRAN Command to the UE 101, the source RNC 104 waits for asuitable time period to clear buffers. In one example, the time periodmay be a few hundreds of millisecond. Different from the related art,the P-GW 118 may start forwarding packets to the eUTRAN before the UE101 has been asked to handover from the UTRAN to the eUTRAN (i.e.,before receiving the HO from UTRAN Command).

In one example, the source RNC 104 may send a suitable message (e.g., apre-HO message) 1208 to the target eNB 112 via a suitable dataconnection. Responsive to the pre-HO message 1208, the target eNB 112informs the target MME 114 by sending the message Handover Notify(TAI+ECGI) 1210. Then, the target MME 114 informs the source SGSN 109 bysending the Forward Relocation Complete Notification message 1212. Thesource SGSN 109 also sends an acknowledge message 1214 to the target MME114. The target MME 114 will now commerce the Inter-RAT handoverprocedure by informing the S-GW 116 that the target MME 114 is nowresponsible for all the bearers the UE 101 have established. This isperformed in the message Modify Bearer Request 1216.

The S-GW 116 acknowledges the user plane switch to the target MME 114via the message Modify Bearer Response 1218. At this stage, the P-GW 118may start forwarding packets to the eUTRAN side (e.g., eNB 112) beforethe UE 101 receives the message HO from UTRAN Command 1220 from thesource RNC 104. Subsequently, when the UE 101 has access to the targeteNB 112, the UE 101 sends the message HO to eUTRAN Complete 1222 to thetarget eNB 112. Accordingly, packet dropping may be avoided during thehandover from the UTRAN to the eUTRAN because data can be sent using theeUTRAN before the UE 101 is moved from the UTRAN to the eUTRAN. Theabove-described handover procedures illustrate some of the relevanthandover steps when the UE 101 is moved from the UTRAN to the eUTRANaccording to some aspects of the disclosure. Other steps or processesthat are generally known in the art are omitted for reasons of clarityand comprehensibility. Furthermore, the handover procedures illustratedin FIG. 12 may be applicable in other Inter-RAT handovers, and thepresent disclosure is not limited thereto.

The handover procedures illustrated in FIG. 12 calls for a change in theorder of the message HO from UTRAN Command 1220 sent to the UE 101 andother messages for switching the user plane to the target eNB 112.Therefore, the user plane data connection may be switched from thesource RNC 104 to the target eNB 112 earlier than that of the relatedart (e.g., FIG. 11). As those skilled in the art will readilyappreciate, various aspects described throughout this disclosure may beextended to other telecommunication systems, network architectures andcommunication standards.

Several aspects of a wireless telecommunications system have beenpresented with reference to a UTRAN/eUTRAN system. As those skilled inthe art will readily appreciate, various aspects described throughoutthis disclosure may be extended to other telecommunication systems,network architectures and communication standards.

By way of example, various aspects may be extended to other UMTS systemssuch as TD-SCDMA and TD-CDMA. Various aspects may also be extended tosystems employing Long Term Evolution (LTE) (in FDD, TDD, or bothmodes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000,Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB),Bluetooth, and/or other suitable systems. The actual telecommunicationstandard, network architecture, and/or communication standard employedwill depend on the specific application and the overall designconstraints imposed on the system.

It is to be understood that the specific order or hierarchy of steps inthe methods disclosed is an illustration of exemplary processes. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the methods may be rearranged. The accompanyingmethod claims present elements of the various steps in a sample order,and are not meant to be limited to the specific order or hierarchypresented unless specifically recited therein.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but are to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. A phrase referring to“at least one of” a list of items refers to any combination of thoseitems, including single members. As an example, “at least one of: a, b,or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, band c. All structural and functional equivalents to the elements of thevarious aspects described throughout this disclosure that are known orlater come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

What is claimed is:
 1. A method of wireless communication, comprising:transferring data at a network controller for a user equipment via afirst user plane connection in a first radio access network; andinitiating a handover procedure of transferring the user equipment to asecond user plane connection in a second radio access network, whereinthe handover procedure comprises: initiating the second user planeconnection for the user equipment in the second radio access networkprior to transmitting a handover command to the user equipment; andtransmitting the handover command to the user equipment to release thefirst user plane connection.
 2. The method of claim 1, wherein the firstradio access network comprises a UMTS terrestrial radio access network(UTRAN).
 3. The method of claim 2, wherein the second radio accessnetwork comprises an evolved UTRAN (E-UTRAN).
 4. The method of claim 1,further comprising if an amount of the data transferred via the firstuser plane connection exceeds a first threshold value during a period oftime, initiating the handover procedure.
 5. The method of claim 1,further comprising: receiving at the network controller from the userequipment a signal quality indication of the second radio accessnetwork; and if the signal quality indication exceeds a second thresholdvalue, initiating the handover procedure.
 6. The method of claim 5,wherein the signal quality indication comprises an evolved UMTSterrestrial radio access (E-UTRA) reference signal receiver quality(RSRQ), an E-UTRA reference signal received power (RSRP), or acombination thereof.
 7. An apparatus for wireless communication,comprising: means for transferring data for a user equipment via a firstuser plane connection in a first radio access network; and means forinitiating a handover procedure of transferring the user equipment to asecond user plane connection in a second radio access network, whereinthe means for initiating the handover procedure comprises: means forinitiating the second user plane connection for the user equipment inthe second radio access network prior to transmitting a handover commandto the user equipment; and means for transmitting the handover commandto the user equipment to release the first user plane connection.
 8. Theapparatus of claim 7, wherein the first radio access network comprises aUMTS terrestrial radio access network (UTRAN).
 9. The apparatus of claim8, wherein the second radio access network comprises an evolved UTRAN(E-UTRAN).
 10. The apparatus of claim 7, wherein if an amount of thedata transferred via the first user plane connection exceeds a firstthreshold value during a period of time, the means for initiating thehandover procedure is configured to initiate the handover procedure. 11.The apparatus of claim 7, further comprising: means for receiving fromthe user equipment a signal quality indication of the second radioaccess network; and wherein if the signal quality indication exceeds asecond threshold value, the means for initiating the handover procedureis configured to initiate the handover procedure.
 12. The apparatus ofclaim 11, wherein the signal quality indication comprises an evolvedUMTS terrestrial radio access (E-UTRA) reference signal receiver quality(RSRQ), an E-UTRA reference signal received power (RSRP), or acombination thereof.
 13. A computer-readable storage medium comprisingcode for causing a network controller to: transfer data for a userequipment via a first user plane connection in a first radio accessnetwork; and initiate a handover procedure of transferring the userequipment to a second user plane connection in a second radio accessnetwork, wherein in the handover procedure, the network controller isconfigured to: initiate the second user plane connection for the userequipment in the second radio access network prior to transmitting ahandover command to the user equipment; and transmit the handovercommand to the user equipment to release the first user planeconnection.
 14. The computer-readable storage medium of claim 13,wherein the first radio access network comprises a UMTS terrestrialradio access network (UTRAN).
 15. The computer-readable storage mediumof claim 14, wherein the second radio access network comprises anevolved UTRAN (E-UTRAN).
 16. The computer-readable storage medium ofclaim 13, wherein the network controller is further configured to if anamount of the data transferred via the first user plane connectionexceeds a first threshold value during a period of time, initiate thehandover procedure.
 17. The computer-readable storage medium of claim13, wherein the network controller is further configured to: receivefrom the user equipment a signal quality indication of the second radioaccess network; and if the signal quality indication exceeds a secondthreshold value, initiate the handover procedure.
 18. Thecomputer-readable storage medium of claim 17, wherein the signal qualityindication comprises an evolved UMTS terrestrial radio access (E-UTRA)reference signal receiver quality (RSRQ), an E-UTRA reference signalreceived power (RSRP), or a combination thereof.
 19. An apparatus forwireless communication, comprising: at least one processor; and a memorycoupled to the at least one processor, wherein the at least oneprocessor is configured to: transfer data for a user equipment via afirst user plane connection in a first radio access network; andinitiate a handover procedure of transferring the user equipment to asecond user plane connection in a second radio access network, whereinin the handover procedure, the at least one processor is configured to:initiate the second user plane connection for the user equipment in thesecond radio access network prior to transmitting a handover command tothe user equipment; and transmit the handover command to the userequipment to release the first user plane connection.
 20. The apparatusof claim 19, wherein the first radio access network comprises a UMTSterrestrial radio access network (UTRAN).
 21. The apparatus of claim 20,wherein the second radio access network comprises an evolved UTRAN(E-UTRAN).
 22. The apparatus of claim 19, wherein the at least oneprocessor is further configured to if an amount of the data transferredvia the first user plane connection exceeds a first threshold valueduring a period of time, initiate the handover procedure.
 23. Theapparatus of claim 19, wherein the at least one processor is furtherconfigured to: receive from the user equipment a signal qualityindication of the second radio access network; and if the signal qualityindication exceeds a second threshold value, initiate the handoverprocedure.
 24. The apparatus of claim 23, wherein the signal qualityindication comprises an evolved UMTS terrestrial radio access (E-UTRA)reference signal receiver quality (RSRQ), an E-UTRA reference signalreceived power (RSRP), or a combination thereof.